Many voters have already made up their minds about who they will vote for in November. Indeed, for the reddest of the red and the bluest of the blue, there was never any doubt about how they would cast their ballots. But interestingly, as the country has grown more and more polarized over the past half century, more and more voters have rejected partisan identities altogether, choosing to call themselves Independents. Some polls put the number of Independent voters as high as four in ten today, which means that the next President will be the candidate who captures the minds of this vast middle.

But who are these so-called Independents? And how many true Independents are there? Some self-labeled Independents will concede, if nudged by pollsters, that they “lean” toward Democrats or toward Republicans, but many more insist they are truly objective, above the partisan fray—ruggedly self-reliant like the nation’s pioneers. How do they manage to rise above party politics while the rest of the electorate is divided by ideology?

Well, perhaps they don’t. New evidence suggests that the label Independent may imply more objectivity and purity than these Independents deserve. Two psychological scientists at the University of Virginia, Carlee Beth Hawkins and Brian Nosek, decided not to take Independents at their word, but instead to probe the unconscious biases that churn deep inside the Independent mind.

The scientists used a tool called the Implicit Association Test, or IAT, which allows them to dig below conscious awareness and intention to uncover hidden preferences, in this case hidden preferences for Democratic or Republican identity and ideas. Nobody likes to think their decision making is predictable or automatic, but that’s precisely what the IAT posits and measures—unconscious partisan leanings and, what’s more, predictable political judgments on important policy issues.

Here’s one example of how they tested this idea. A random sample of more than 1800 volunteers participated on the Project Implicit website, where they read a mock newspaper article comparing two competing welfare proposals. One plan was generous in its benefits, the other much more stringent. Some of the volunteers read an article that said the Democrats were supporting the generous plan; Republicans, the stringent plan. The others read the same article, but with the parties switched around.

All the volunteers recorded their policy preferences, and also described their political ideology and their party identification, including Independent. Those who selected Independent were asked if they leaned toward either of the two major parties. The only pure Independents were those who did not indicate even a leaning toward Democrat or Republican identity.

Note that these were the explicit measures of the volunteers’ identity, ideology and position on welfare. Next the volunteers took a version of the IAT measuring implicit associations. That is, the test spotted partisan identities that the volunteers themselves might be unaware of, and also preferences for welfare policies that they may or may not have articulated even to themselves. The idea was to see if Independents had unacknowledged partisan identities, and if these identities influenced their thinking about policy.

The results were intriguing—and politically significant. As Hawkins reported this week at the annual meeting of the Association for Psychological Science, in Chicago, self-proclaimed Independents are not as independent-minded as they claim they are. In fact, Independents vary greatly in their unconscious partisanship, and they make partisan political judgments in line with their implicit political identities. Among the self-proclaimed Independents, those who unconsciously identified with Democrats preferred the liberal welfare plan, while the implicit Republicans had a clear preference for the conservative welfare plan. In other words, they acted like liberal Democrats and conservative Republicans even if they refused to accept any political labels.

They also acted like blinkered partisans. Independents who were implicitly Republican preferred whatever plan was proposed by Republicans—regardless of the values underlying the plan—more than they favored any plan proposed by Democrats. The same was true for implicit Democrats, and this partisanship was much more powerful at the unconscious level. Despite their claims of disinterested objectivity, self-identified Independents appear to be influenced both by ideology and by partisanship when it comes to making policy judgments.

It appears that Independents identify themselves as Independents because they want to appear objective. It’s a socially desirable label. But inside most Independents is a partisan of some stripe. If this is the case—if even the purest of Independents have already chosen a party and candidate to back—then the election may already be over.

Wray Herbert’s book, On Second Thought, is about irrational thinking and judgment. Excerpts from his two blogs, “Full Frontal Psychology” and “We’re Only Human”—appear regularly in The Huffington Post and in Scientific American Mind.